#include<stdio.h>

int main()
{
	double pool;
	float A,B,C,D;
	float sum=0;
	B=1.0;
	//四个水渠一天注水量之和
	sum=B/3+B/4+B/5+B;
	
	printf("需要%lf天",1.0/sum);

	
	return 0;
}